System and method for triggering an imaging process based on non-periodicity in breathing

ABSTRACT

A method of triggering an imaging process includes obtaining breathing signals, analyzing the breathing signals to identify a non-periodicity in a subject&#39;s breathing, and generating a signal to cause an imaging process to begin in response to the identified non-periodicity. A computer product having a set of instructions stored in a non-transitory medium, wherein an execution of the instructions causes a method to be performed, the method includes obtaining breathing signals, analyzing the breathing signals to identify a non-periodicity in a subject&#39;s breathing, and generating a signal to cause an imaging process to begin in response to the identified non-periodicity. A system for triggering an imaging process includes a processor that is configured for obtaining breathing signals, analyzing the breathing signals to identify a non-periodicity in a subject&#39;s breathing, and generating a signal to cause an imaging process to begin in response to the identified non-periodicity.

FIELD

This invention relates to systems and methods for processing breathingsignals, and to systems and methods that use the results of theprocessing of breathing signals.

BACKGROUND

Radiation therapy has been employed to treat tumorous tissue. Inradiation therapy, a high energy beam is applied from an external sourcetowards the patient. The external source, which may be rotating (as inthe case for arc therapy), produces a collimated beam of radiation thatis directed into the patient to the target site. The dose and placementof the dose must be accurately controlled to ensure that the tumorreceives sufficient radiation, and that damage to the surroundinghealthy tissue is minimized.

Sometimes during a radiation therapy, the patient may be undergoingbreathing motion. In such cases, it may be desirable to compensate forbreathing motion during the treatment delivery session such thatradiation may be properly delivered, or ceased to be delivered, to thetarget region. For example, if the patient's breathing becomesnon-periodic (e.g., due to sudden movement such as coughing), then itmay be desirable to stop a delivery of radiation. Compensating forbreathing motion has two components: 1) determining the location ofradiotherapy target, and 2) controlling component(s) of a radiationsystem, e.g., by turning the therapy beam on-off as in gating,redirecting the beam as in multi-leaf collimator (MLC) tracking, movingthe patient support as in couch tracking, or a combination of the above.

There is a latency associated with current techniques of localizing thetarget. This is because current localization methods have a latencyresulting from data acquisition and another latency resulting from theprocessing delays. There is also latency in the controlling of thecomponents of a radiation system, such as mechanical motion required toeither redirect the treatment beam or to reposition the patient.Applicant determines that in order to make the compensation forbreathing motion temporally and geometrically accurate the overalllatency from both the target localization and the controlling of machinecomponents need to be overcome. In order to compensate for breathingmotion, Applicant determines that it would be desirable to provide newtechniques for predicting breathing signal, so that the overall latencyfrom target localization and controlling of machine components can beovercome.

Also, unconstrained and normal breathing motion of a lung target is onlyapproximately periodic and subject to variation in time. These changescan be a combination of baseline drift and breath-to-breath changes inamplitude and period in the order of 10 percent or more. More suddenchanges caused by coughing or swallowing will result in even largerdeviations from the normal breathing pattern. Sometimes, audio or visualcoaching techniques can reduce these variations, but a 10 percent changeis normal even after implementing these techniques in the clinic.Applicant of the subject application determines that there is a need toquantify the degree of non periodicity of breathing resulting from abovevariations, since it is expected to affect the performance of anyprediction algorithm, and therefore the accuracy of determining thetarget position for management of motion. Also Applicant determines thatit would be desirable to have a fast responding and prospective measureof non periodicity that can be used to interrupt the treatment beam whena sudden deviation from normal breathing pattern occurs. In order tocompensate for deviation from periodicity (e.g., due to coughing),Applicant determines that it would be desirable to provide newtechniques for determining non-periodicity.

Also, in current radiation therapy techniques, the internal targetregion is periodically imaged (e.g., using x-ray) to verify the positionof the internal target region during a treatment session. Applicantdetermines that periodically imaging of internal target region is notdesirable because it increases radiation dose delivered to the patient.Thus, Applicant also determines that it would be desirable to provide atechnique for triggering imaging process that is non-periodic.

SUMMARY

In accordance with some embodiments, a method of triggering an imagingprocess includes obtaining breathing signals, analyzing the breathingsignals to identify a non-periodicity in a subject's breathing, andgenerating a signal to cause an imaging process to begin in response tothe identified non-periodicity.

In accordance with other embodiments, a computer product having a set ofinstructions stored in a non-transitory medium, wherein an execution ofthe instructions causes a method to be performed, the method includesobtaining breathing signals, analyzing the breathing signals to identifya non-periodicity in a subject's breathing, and generating a signal tocause an image process to begin in response to the identifiednon-periodicity.

In accordance with other embodiments, a system for triggering an imagingprocess includes a processor that is configured for obtaining breathingsignals, analyzing the breathing signals to identify a non-periodicityin a subject's breathing, and generating a signal to cause an imageprocess to begin in response to the identified non-periodicity.

Other and further aspects and features will be evident from reading thefollowing detailed description of the embodiments, which are intended toillustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of embodiments, in whichsimilar elements are referred to by common reference numerals. Thesedrawings are not necessarily drawn to scale. In order to betterappreciate how the above-recited and other advantages and objects areobtained, a more particular description of the embodiments will berendered, which are illustrated in the accompanying drawings. Thesedrawings depict only typical embodiments and are not therefore to beconsidered limiting of its scope.

FIG. 1 illustrates a breathing monitoring system in accordance with someembodiments;

FIG. 2 illustrates a method of processing breathing signals to determinenon-periodicity in breathing in accordance with some embodiments;

FIG. 3 is an exemplary chart showing phase and amplitude for a periodicsignal;

FIG. 4 illustrates an example of a signal-phase histogram;

FIG. 5 illustrates a concept of determining reference value(s) in asignal-phase histogram;

FIG. 6 illustrates a radiation system that uses the breathing monitoringsystem of FIG. 1 in accordance with some embodiments;

FIG. 7 illustrates a method of triggering an imaging procedure inaccordance with some embodiments;

FIG. 8 illustrates another radiation system that uses the breathingmonitoring system of FIG. 1 in accordance with other embodiments;

FIG. 9 illustrates another radiation system that uses the breathingmonitoring system of FIG. 1 in accordance with other embodiments; and

FIG. 10 is a block diagram of a computer system architecture, with whichembodiments described herein may be implemented.

DESCRIPTION OF THE EMBODIMENTS

Various embodiments are described hereinafter with reference to thefigures. It should be noted that the figures are not drawn to scale andthat elements of similar structures or functions are represented by likereference numerals throughout the figures. It should also be noted thatthe figures are only intended to facilitate the description of theembodiments. They are not intended as an exhaustive description of theinvention or as a limitation on the scope of the invention. In addition,an illustrated embodiment needs not have all the aspects or advantagesshown. An aspect or an advantage described in conjunction with aparticular embodiment is not necessarily limited to that embodiment andcan be practiced in any other embodiments even if not so illustrated.

FIG. 1 illustrates a breathing monitoring system 10 in accordance withsome embodiments. The breathing monitoring system 10 includes a camera12, a processor 14 communicatively coupled to the camera 12, a monitor16, and an input device 18. The camera 12 is oriented to view towards apatient 20. In the illustrated embodiments, a marker block 30 is placedon the patient 20, and the camera 12 is positioned so that it can viewthe marker block 30. The processor 14 is configured to process imagesignals (an example of breathing signals) from the camera 12, andprocess the image signals to thereby monitor the breathing of thepatient 20. In some embodiments, the image signals and/or results of theprocessing of the image signals may be displayed on the monitor 16, forallowing a user to view them. Also, in some embodiments, the user mayuse the input device 18 to input parameters for processing of the imagesignals. In other embodiments, the monitor 16 and the input device 18are not necessary, and the device 10 does not include components 16, 18.

As shown in the figure, the marker block 30 includes a plurality ofmarkers 32 that are viewable by the camera 12. Each marker 32 mayinclude a reflective material so that it can be more easily detected bythe camera 12. In the illustrated embodiments, the relative positionsamong the markers 32 are predetermined. The processor 14 is configuredto determine the position of the marker block 30 using the predeterminedrelative positions of the markers 32. In particular, the processor 14 isconfigured to compare the pattern of the markers 32 in the imageprovided by the camera 12 with known pattern of the markers 32 based onthe predetermined relative positions of the markers 32. Based on thecomparison, the processor 14 then determines the position of the markerblock 30. By continuously processing image signals and determining theposition of the marker block 30, the processor 14 can determine thebreathing amplitude of the patient 20 in substantially real time.

FIG. 2 illustrates a method 200 of processing breathing signals inaccordance with some embodiments. In the illustrated embodiments, themethod 200 is performed by the system 10 (e.g., processor 14) of FIG. 1.First, breathing signals of the patient are obtained (step 202). In someembodiments, such may be accomplished by the processor 14 receivingimage signals from the camera 12, wherein the image signals themselvesmay be considered breathing signals. In other embodiments, image signalsare processed by the processor 14 to determine breathing amplitudes. Insuch cases, the breathing amplitudes may be considered breathingsignals, and the act of obtaining breathing signals may be accomplishedby processing the image signals to determine breathing amplitudes usingthe processor 14. In other embodiments, instead of using the camera 12(which does not involve any radiation) to obtain the image signals, theimage signals may be obtained using a radiation source (e.g., x-ray, CT,etc.), or other imaging devices, such as MRI, ultrasound, etc. It shouldbe noted that as used in this specification, the term “breathing signal”or similar term may refer to any information that may represent, or thatmay be used to determine, a breathing state or a breathingcharacteristic of a subject.

Next, the processor 14 determines a signal-phase histogram using thebreathing signals (step 204). In the illustrated embodiments, thesignal-phase histogram includes a plurality of data points, with each ofthe data points having at least a phase value and a signal value. In oneimplementation, for each breathing amplitude (which may be a position ofany bodily part that moves due to breathing, a position of an objectcoupled to such bodily part, or any signal that is associated withbreathing), the processor 14 determines a corresponding breathing phasefor the breathing amplitude. The phase of a physiological cyclerepresents a degree of completeness of a physiological cycle. In someembodiments, the phases of a respiratory cycle may be represented by aphase variable having values between 0° and 360°. FIG. 3 illustrates anexample of a phase diagram 300 that is aligned with a correspondingamplitude/position diagram 302. Amplitude diagram 302 includespositional points of the marker block 30 determined using embodiments ofthe technique described herein. Each point in the amplitude diagram 302represents a position of the marker block 30 or a bodily part at acertain point in time. In the illustrated example, a phase value of 0°(and 360°) represents a peak of an inhale state, and the phase valuevaries linearly between 0° and 360° in a physiological cycle. As shownin the diagram, for each point in the amplitude diagram 302 at certainpoint in time, a corresponding phase value at the same point in time maybe obtained. Thus, for each breathing amplitude, the processor 14 candetermine the corresponding phase of the respiratory cycle. In someembodiments, the determined phase may be considered an example of abreathing signal. In such cases, the act of determining the phase by theprocessor 14 may be performed in step 202 to obtain the breathingsignal.

In the illustrated embodiments, as the patient 20 is undergoingbreathing, the processor 14 continues to determine data points (signal,phase), with the signal representing a breathing amplitude. The datapoints are collected over time using the system 10, and are then used togenerate the signal-phase histogram. FIG. 4 illustrates an example of asignal-phase histogram 400 that is generated using the above technique.In the example of the signal-phase histogram 400, the x-axis representsphase values ranging from 0 to 2π, and the y-axis represents amplitude(or signal) values. In other embodiments, the x-axis may representamplitude (or signal) values, and the y-axis may represent phase values.In one technique, the histogram 400 is implemented as an array having a64-times-64 array of bins covering the range of phase values (from 0 to2π) in the horizontal dimension, and the range of respiration signalamplitudes in the vertical dimension. The amplitude and phase of eachnew sample are used to increment the corresponding bin in histogramarray 400. In other embodiments, the array may have different sizes. Forexample, in other embodiments, the array may have a 128-times-128 arrayof bins.

In some embodiments, the processor 14 is configured to update thehistogram 400 by disregarding data points that are older than aprescribed period. In some cases, the prescribed period may bedetermined by a user, and input into the processor 14 using the inputdevice 18. For example, a user interface may be provided in the screen16 that allows the user to enter a time (t), or a number of breathingcycles (N), each of which may be considered an example of a prescribedperiod. For each data point on the histogram 400 that is determined bythe processor 14, the processor 14 also time stamps the data point—e.g.,by assigning a time value or a breathing cycle number, to identify whenthe data point was determined. During the breathing monitoring process,the processor 14 is configured to decrement the bins in the histogram400 having data points that are older than the prescribed period. Forexample, if a data point at a bin is time stamped with a breathing cyclenumber of “2,” and the current breathing cycle is at “6,” and assumingthat the prescribed period is 4 cycles (meaning that the histogram 400will not include data points that are older than 4 cycles), then theprocessor 14 will update the bin by decrementing a count value todisregard the data point because the data point is for a breathing cyclethat occurred more than 4 cycles ago. In the illustrated embodiments,the prescribed period may be selected by a user, and may be input by theuser. The above technique prevents the processor 14 from determiningthat there is non-periodicity in the breathing due to slow variation inthe breathing pattern, thereby allowing slow variation in the patient'sbreathing during the breathing monitoring process.

Returning to the method 200 of FIG. 2, next, the processor 14 determinesreference value(s) using at least some of the plurality of data pointsfrom the signal-phase histogram (step 206). In some embodiments, areference value may be determined by obtaining an average of the signalvalues for a given phase value in the histogram array 400. For example,if phase bin that corresponds to phase value of P or phase range P1-P2has signal values of S1, S2, and S3, then the reference value may bedetermined as the average of these three signal values. In otherembodiments, the number of count in each bin of the histogram array 400may be used to determine a weighted average, which weighted average isthen used as the reference value. In the above example, if signal valueS3 has three counts, and S1 and S2 each has one count in the bin of thehistogram array 400, then signal value S3 may be given more weight indetermining the weighted average. In the above embodiments, thereference values for the respective phase bins of the histogram 400 areaverage values. In other embodiments, the reference values may be medianvalues (e.g., weighted median values) for the respective phase bins inthe histogram 400.

In other embodiments, the average or median of signal values for thecurrent phase is calculated only over the prior breathing cycles, andthe current signal value is not used in calculating the average or themedian. For example, in one implementation, the average or median iscalculated before the current signal-phase bin in the histogram isincremented. This technique allows deviation from previous cycles to bedetermined.

In other embodiments, the determined reference values in the histogram400 may optionally be used to determine a reference curve that best fitthrough and/or among the reference values. For example, in theembodiments in which the reference values are average values, the bestfit curve represents the average values for different respective phasevalues. In the embodiments in which the reference values are medianvalues, the best fit curve then represents the median values fordifferent respective phase values.

Next, the processor 14 determines whether a difference between thereference value and a signal value that is associated with a currentrespiratory cycle exceeds a threshold (step 208). The threshold ispredetermined (e.g., it may be arbitrarily set by a user of the system10), and may be input by the user using the input device 18. In otherembodiments, the threshold may be preprogrammed into the processor 18.

One implementation of the action 208 is illustrated in the example ofFIG. 5. As shown in the figure, data points 510 represented by thedashed line are from the current respiratory cycle, with data points 512being the latest data point that has been obtained (e.g., data point atthe current time instant). Data points 520 in the histogram 500 are fromthe previous respiratory cycles. The histogram 500 also has a solid line528 representing reference values for different respective phase valuesthat are determined in step 206. The latest data point 512 used toupdate the histogram 500 has signal value 514 and an associated phase(or phase bin) value 516. In the illustrated example, for the phasevalue 516 that is associated with the latest signal 514, the histogram500 has a corresponding reference signal value 530 that is determinedfrom step 206. In step 208, the processor 14 compares the signal 514with the reference signal value 530 (e.g., by determining the differenceΔ(t) between the two).

In the illustrated embodiments, if the difference Δ(t) between thereference value 530 and the signal value 514 exceeds the threshold, theprocessor 14 then generates an output (e.g., a signal) (step 210),indicating that there is non-periodicity in the patient's breathing. Forexample, the processor 14 may generate an output to activate an audiodevice to cause the audio device to emit an audio signal. In anotherexample, the processor 14 may generate an output to cause information bedisplayed on the monitor 16. In other embodiments, the processor 14 maygenerate an output to use and/or control a device, such as a treatmentradiation machine, or an imaging device.

In the above embodiments, deviation Δ(t) of the latest signal value 514from average or median 530 over past cycles at the corresponding latestphase 516 is used to determine non-periodicity (e.g., it is used as thevalue of non-periodicity). In particular, the deviation Δ(t) from thelatest data point in the recent history is used without change as themeasure of deviation from periodicity. In such technique, the processor14 does not extrapolate the deviation based on the recent history ofdeviations.

In other embodiments, instead of using Δ(t) from the latest data pointwithout change, the processor 14 is configured to extrapolate thedeviation based on the recent history of the deviations. In such cases,the processor 14 is configured to analyze the data points in the recenthistory, and use the pattern of deviations to extrapolate the deviation.For example, the processor 14 may use linear extrapolation to determinethe deviation. In this embodiment of prediction, the extrapolated valuecan be used as the value of non-periodicity. In other embodiments,instead of linear extrapolation, other degrees of extrapolation may beused.

It should be noted that the measure of non-periodicity (whether forwardextrapolation from recent history is used or not) is “prospective”because there is no need to wait and retrospectively see how well theprediction works in order to get a measure on periodicity.

In some embodiments, the difference signal Δ(t) (the difference betweenthe current signal sample and the prior cycles cluster average) fordetermining the measure of non-periodicity may also be used to estimatea breathing signal. In some cases, it may be useful to predict abreathing signal in a future time in order to compensate for any latencythat may exist in a radiation system. For example, in some embodiments,if it is desirable to deliver radiation (e.g., treatment radiation orimaging radiation) when the subject is at breathing state X, andassuming that it may take a radiation system a duration of P to activatethe various components to deliver the radiation beam, then it may beuseful to predict the breathing state at least P ahead of time so thatthe latency of the radiation system may be compensated. This isbeneficial because this may allow the radiation beam to be deliveredprecisely at the appropriate time when the subject is at breathing stateX.

The concept of predicting the signal value at a forward time isillustrated in FIG. 5. In the figure, the future breathing signal 550 ispredicted for a future phase 560 by taking the difference (Δ(t)) betweenthe latest signal 514 and the reference value 530, and applying the samedifference for the future phase 560. In particular, the same differenceis added to the reference value 562 at the future phase 560 to obtainthe predicted future breathing signal 550. It should be noted that howmuch the phase value needs to be forwarded (i.e., the phase differencebetween value 560 and value 516) depends on how much latency needs to becompensated, i.e., how much forward prediction is needed. In someembodiments, the amount of forward phase may be entered as an input tothe processor 14 by a user. For a given latency time P that needs to becompensated, the corresponding phase difference (P/T*360°) can bedetermined by the processor 14. In other embodiments, instead of usingΔ(t) from the latest data point without change for predicting thebreathing signal, the processor 14 is configured to extrapolate thedeviation based on the recent history of the deviations (as similarlydiscussed with reference to determining measure of non-periodicity) forpredicting the breathing signal. In such cases, the extrapolated valueis added to the reference value 562 at the future phase 560 to obtainthe predicted future breathing signal 550.

The mathematical concepts of determining value of non-periodicity, andprediction of breathing signal, in accordance with some embodiments isnow further discussed with reference to FIG. 5. As discussed, theprocessor 14 is configured to estimate the phase of the breathing cycleφ(t) from the breathing signal s(t) in real time where φ(t) goes from 0at end-inhale to 2π at the following end-inhale. The signal-phasehistogram is formed by accumulating the sample pairs [φ(t),s(t)] in atwo-dimensional (2D) histogram array. Refer back to FIG. 5, which showsa graphical representation of the signal-phase histogram. The processor14 first learns the breathing pattern from the signal-phase clusteringof data samples over 3 to 4 initial breathing cycles. Subsequently, theprocessor 14 produces a continuous and real-time measure of nonperiodicity of breathing. FIG. 5 shows how the pattern of clustering ofsignal-phase samples in the 2D histogram is used to see how far a newsample is from the past history of the signal at any given time.

In FIG. 5, the dashed line trace shows the breathing signal during theongoing breathing cycle where the latest signal-phase sample [φ(t),s(t)]is used to increment the corresponding histogram bin. The signal samplesfor each phase φ is averaged over prior breathing cycles and forms thecluster average function s(φ),[φε(0,2π)]. This function defines theaverage or median breathing pattern up to the latest data point. Notethat since s(φ) is a function of phase rather than time, it allows forvariations of breathing period T which may be estimated by the processor14 in some embodiments. The estimate of T is updated at every newlydetected end-inhale and end-exhale point of the breathing cycle.

For the purpose of predicting the breathing signal at a future time(e.g., future relative to the latest data point), the processor 14 isconfigured to extrapolate the breathing signal forward while conformingto the shape of the average/median breathing pattern defined by thefunction s(φ). For this, the processor 14 uses the current estimate ofperiod T to transform the forward time (t+τ) to the forward phase[φ(t)+2πτ/T](mod 2π). In some embodiments, the difference signalΔ(t)≈s(t)− s[φ(t)] may be defined as the difference between the currentsignal sample and the prior cycles cluster average. In order to obtainthe forward predicted signal value s(t+τ), the processor 14 extrapolatesΔ(t) forward in time and then add it to the prior cluster average at theforward phase [φ(t)+2πτ/T](mod 2π):s (t+τ)= s {[φ(t)+2πτ/T](mod 2π)}+{circumflex over (Δ)}(t+τ)where {circumflex over (Δ)}(t+τ) is the forward extrapolation of Δ(t),and s{[φ(t)+2πτ/T](mod 2π)} is the prior cluster average at the forwardphase [φ(t)+2πτ/T](mod 2π). The forward extrapolation of Δ(t) can be azero-order extrapolation where {circumflex over (Δ)}(t+τ)=Δ(t) or it canbe higher order such as linear extrapolation using most recent samplesof Δ(t) over a short period, e.g., 0.5 Sec.

In some embodiments, the real-time signal defining the measure of nonperiodicity is defined as the absolute value of {circumflex over(Δ)}(t+τ), that is the forward extrapolated difference between signaland the prior cluster average N_(τ)(t)≈|{circumflex over (Δ)}(t+τ)|.

The non periodicity function N_(τ)(t) is a real-time signal parallel tothe breathing signal s(t) which can be used prospectively as anindication of breathing behavior at time (t+τ). As such, it can be usedto trigger a prescribed action, such as beam-hold or image acquisition,in response to irregular breathing. It should be noted that forzero-order extrapolation of the deviations, the difference functionN_(T)(t) does not depend on τ, but for linear and higher orderextrapolation, it depends on the length of forward prediction time.

As discussed above with reference to the method 200 of FIG. 2,non-periodicity of breathing may be quantified (measured) in the form ofa secondary signal derived in real time from the breathing signal. Theinstantaneous prediction error associated with the above predictiontechnique is the difference between s(t), the actual signal at time t,and the signal ŝ(t) predicted τ seconds earlier. This can beretrospectively defined as φ_(τ)(t)≈s(t)−ŝ(t). One possible measure ofprediction error is defined as the root mean square (RMS) value of thisdifference

${E\left( {\tau,W} \right)}\overset{\Delta}{=}\sqrt{\frac{1}{n_{w}}{\sum\limits_{t \in W}{{e_{\tau}(t)}}^{2}}}$It is calculated over a specified time window W of n_(W) samples thatcan for example be the length of a treatment session. It has beendetermined that the method 200 of FIG. 2 provides a high correlationbetween non-periodicity measure and prediction error for differentforward times that range from 200 mSec to at least 700 mSec. Also, usingthe method 200 of FIG. 2 for different forward times, it has beendetermined that the prediction errors correlate well with differentrespective forward times.

In some embodiments, embodiments of the above technique for predictingsignal value yields a prediction error of 1.75 mm (e.g., differencebetween actual position/amplitude and predicted position/amplitude) orless for 350 mSec of forward extrapolation time, and yields a predictionerror of 2.5 mm or less for 500 mSec of forward extrapolation time,wherein the prediction errors are expressed in terms of amplitude (orposition) that is associated with the patient's breathing. In someembodiments, the forward time may be an input to the algorithm. Theforward time can be anything from very small, even zero, to over severalseconds. The prediction error increases with forward time, but comparedto existing techniques, it increases relatively less. For example, aforward prediction time of 200 mSec may be sufficient to overcome thelatency associated with target localization and the latency associatedwith the controlling of component(s) in some radiation machines. Inother cases, the forward extrapolation time (e.g., how far in the futurethe target position needs to be predicted) may be other values,depending on the technique of target localization, the component(s) ofthe radiation machine and imaging systems that needs to be controlled,and their respective latencies that need to be overcome.

In the above embodiments, the camera 14 has been described as beingconfigured to view the marker block 30. In other embodiments, the markerblock 30 is not necessary, in which case, the camera 14 may be used toview the patient 20. For examples, the camera 14 may be used to view thebody of the patient 20, the clothes of the patient 20, and/or a blanketthat is covering the patient 20. In these embodiments, the processor 14is configured to perform image processing to identify landmark(s) in theimages to thereby determine breathing information (e.g., breathingamplitudes, breathing phase, etc.) for the patient 20.

In the above embodiments, the system 10 is described as having a camera12 for obtaining image signals that can be used to determine breathingamplitudes. In other embodiments, the system 10 may not include thecamera 12. Instead, the system 10 may include other types of devices forproviding breathing information. For example, in other embodiments, thesystem 10 may include a strain-gauge that is coupled to the patient 20.In such cases, the strain-gauge is communicatively coupled to theprocessor 14 for providing signals that represent breathing amplitudesof the patient 20. In other embodiments, the system 10 may include asensor coupled to the patient's mouth and/or nose for sensing thebreathing of the patient 20. The processor 14 is communicatively coupledto the sensor, and receives signals from the sensor. The signals mayrepresent the breathing amplitudes, or may be used to obtain breathingamplitudes and/or breathing phases. In some embodiments, the breathingsignal includes the position coordinates of internal anatomy landmarks,the tumor, and/or implanted fiducials. These position coordinates may bemeasured by various methods, including X-ray imaging, MRI, or othertypes of imaging. In further embodiments, internal target tracking maybe employed that uses radio frequency transponder(s) implanted in ornear the target region (e.g., tumor). The transponder(s) is localized byan external array antenna transmitting query signals and processing thetransponder response signals. Other types of breathing sensing devicesmay be used with the processor 14 in other embodiments.

The breathing monitoring system 10 and the method 200 describedpreviously may be used with a variety of medical devices, and in variousdifferent medical procedures. In some embodiments, the breathingmonitoring system 10 may be used with a treatment radiation machine.FIG. 6 illustrates a radiation system 610 that is used with thebreathing monitoring system 10. The system 610 is a treatment systemthat includes a gantry 612, a patient support 614 for supporting apatient, and a control system 618 for controlling an operation of thegantry 612. The gantry 612 is in a form of an arm. The system 610 alsoincludes a radiation source 620 that projects a beam 626 of radiationtowards a patient 628 while the patient 628 is supported on support 614,and a collimator system 622 for controlling a delivery of the radiationbeam 626. The radiation source 620 can be configured to generate a conebeam, a fan beam, or other types of radiation beams in differentembodiments.

In the illustrated embodiments, the radiation source 620 is a treatmentradiation source for providing treatment energy. In other embodiments,in addition to being a treatment radiation source, the radiation source620 can also be a diagnostic radiation source for providing diagnosticenergy for imaging purpose. In such cases, the system 610 will includean imager, such as the imager 680, located at an operative positionrelative to the source 620 (e.g., under the support 614). In furtherembodiments, the radiation source 620 may be a treatment radiationsource for providing treatment energy, wherein the treatment energy maybe used to obtain images. In such cases, in order to obtain imagingusing treatment energies, the imager 680 is configured to generateimages in response to radiation having treatment energies (e.g., MVimager). In some embodiments, the treatment energy is generally thoseenergies of 160 kilo-electron-volts (keV) or greater, and more typically1 mega-electron-volts (MeV) or greater, and diagnostic energy isgenerally those energies below the high energy range, and more typicallybelow 160 keV. In other embodiments, the treatment energy and thediagnostic energy can have other energy levels, and refer to energiesthat are used for treatment and diagnostic purposes, respectively. Insome embodiments, the radiation source 620 is able to generate X-rayradiation at a plurality of photon energy levels within a range anywherebetween approximately 10 keV and approximately 20 MeV. In furtherembodiments, the radiation source 620 can be a diagnostic radiationsource. In the illustrated embodiments, the radiation source 620 iscoupled to the arm gantry 612. Alternatively, the radiation source 620may be located within a bore.

In the illustrated embodiments, the control system 618 includes aprocessor 654, such as a computer processor, coupled to a control 640.The control system 618 may also include a monitor 656 for displayingdata and an input device 658, such as a keyboard or a mouse, forinputting data. The operation of the radiation source 620 and the gantry612 are controlled by the control 640, which provides power and timingsignals to the radiation source 620, and controls a rotational speed andposition of the gantry 612, based on signals received from the processor654. Although the control 640 is shown as a separate component from thegantry 612 and the processor 654, in alternative embodiments, thecontrol 640 can be a part of the gantry 612 or the processor 654. Theprocessor 654 may be the processor 14, or may include featuresimplemented in the processor 14 of the breathing monitoring system 10.In such cases, the radiation system 610 and the breathing monitoringsystem 10 share the same processor or parts of a same processor.Alternatively, the processor 654 may be a different processor from theprocessor 14.

In some embodiments, when using the system 610 of FIG. 6, the radiationsource 620 is rotated about the patient 628 to deliver treatmentradiation from a plurality of gantry angles, for example, as in arctherapy. As treatment radiation is being delivered to the patient 628,the breathing monitoring system 10 of FIG. 1 may be used to monitor thebreathing of the patient 628. In some embodiments, the processor 654processes the signals from the camera 12 to determine breathingamplitudes of the patient 628, and then gates the delivery of thetreatment radiation based on the amplitudes. For example, the processor654 may cause the radiation source 620 to deliver radiation, or to stopa delivery of radiation, when the determined amplitude is within aprescribed amplitude range. In other embodiments, the processor 654processes the signals from the camera to determine respiratory phases ofthe patient 628, and then gates the delivery of the treatment radiationbased on the respiratory phases. For example, the processor 654 maycause the radiation source 620 to deliver radiation, or to stop adelivery of radiation, when the determined phase is within a prescribedphase range. In further embodiments, the processor 654 processes thesignals from the camera 12 to detect non-periodicity, and then gates thedelivery of the treatment radiation based on the detection ofnon-periodicity. In other embodiments, instead of, or in addition to,controlling the delivery of radiation, the processor 654 may beconfigured to control the gantry 612 (e.g., stop, accelerate, ordecelerate the gantry 612), and/or to position the patient support 614,based on the determined amplitude and/or phase, or detection ofnon-periodicity.

During the treatment process, the processor 654 monitors the patient's628 breathing, and correlates feature(s) of the breathing (such asbreathing signals, breathing amplitudes, breathing phases, etc.) withpositions of internal target region that is being irradiated by theradiation beam 626. For example, based on images received from thecamera 12, the processor 654 then determines the phase/amplitude of thebreathing cycle. The phase of the breathing cycle or the amplitude isthen used by the processor 654 to determine a position of the internaltarget region based on a pre-established relationship between breathingphase/amplitude and position of internal target region. In someembodiments, the relationship between the breathing phase/amplitude andtarget position may be pre-determined by a physician during a treatmentplanning process. For example, during a treatment planning process, itmay be determined that when a patient is at breathing phase=40°, thecorresponding position of the internal target region is at position X=45mm, Y=23 mm, and Z=6 mm relative to the isocenter. This technique allowsthe treatment radiation system 610 to target delivery of radiationtowards the target region based on breathing signals obtained by thesystem 10. Thus, it has the benefit of obviating the need tocontinuously or periodically imaging the internal target region usingX-ray imaging, which may be harmful to the patient due to its additionalradiation dose.

In one method of using the system 10 with the radiation system 610, theprocessor 654 is configured to detect non-periodicity in the patient's628 breathing using the technique described with reference to FIGS. 2-5.When the processor 654 determines that there is non-periodicity in thepatient's 628 breathing, the processor 654 may generate a signal (e.g.,a beam-stop signal) to cause the radiation source 620 to stop deliveringradiation, and/or a signal to control a motion of the gantry 612 (e.g.,to stop the gantry, decelerate the gantry 612, or accelerate the gantry612). By using the above described technique to quantify thenon-periodicity in the form of a secondary signal derived in real timefrom the breathing signal, the system 10 provides a fast responding andprospective measure of non-periodicity that can be used to interrupt thetreatment beam when a sudden deviation from normal breathing patternoccurs. In particular, because the instantaneous value of the measure ofnon-periodicity is a fast acting prospective indication of any deviationfrom normal breathing, the system 10 allows interventions, such asradiotherapy beam-hold, that can be triggered in time.

As discussed, the external optical tracking surrogate signal (e.g.,camera signal) represents the anterior-posterior (AP) displacement ofthe chest or abdomen with patient in supine position. The forwardpredicted value of this one-dimensional signal, along with theinternal-external correlation model, is used by the processor 654 topredict the internal 3D position of the target. Using the camera signalas a surrogate signal to measure internal target position isadvantageous, because it allows the three-dimensional position of theinternal target at a future time to be predicted (estimated) rapidly. Inparticular, because the camera signal is a one-dimensional signal thatcan be obtained and processed quickly, and because the camera provides ahigh sample rate, it provides almost no latency (at least when comparedto latency associated with the controlling of the component(s) of theradiation system 610). However, in other embodiments, the surrogatesignal needs not be a camera signal, and may be other types of signal,as discussed, which may also have a high sample rate.

In other embodiments, as an alternative, or in addition, to controllingcomponent(s) of the radiation system 610, if the radiation system 610has imaging capability, the processor 654 may be configured to generatea signal to trigger an imaging process to image the internal targetregion when the processor 654 determines that there is non-periodicityin the patient's 628 breathing. FIG. 7 illustrates a method 700 oftriggering an imaging process in accordance with some embodiments. Inthe method 700, the processor 654 obtains breathing signals (step 702),and the processor 654 then analyzes the breathing signals to identify anon-periodicity in a subject's breathing (step 704). Embodiments ofperforming the steps 702, 704 are similar to those described previouslywith reference to the method 200.

When the processor 654 determines that there is non-periodicity in thepatient's 628 breathing, the processor 654 then generates a signal tocause an image process to begin (706). In the illustrated embodiments,if the radiation system 610 has imaging capability (e.g., if theradiation system 610 has the imager 680), the image process may beperformed by the system 610. For example, the radiation source 620 maydeliver imaging radiation having diagnostic energy (e.g., in kv range),or radiation having treatment energy level (e.g., in MeV range) togenerate one or more images of the internal region using the imager 680.Alternatively, a separate imaging system may be used to generate theimage(s) of the internal region. For example, the separate imagingsystem may be a CT system, an x-ray system, an ultrasound imagingdevice, a MRI system, a tomosynthesis imaging system, a PET system, aSPECT system, or any other system that is capable of obtaining an imageof the internal target region.

In some embodiments, the image(s) of the internal target region is usedby the processor 654 to verify the position of the target region, and/orto confirm the pre-established relationship between breathing feature(amplitude, phase, etc.) and target position. In other embodiments, theimage of the internal target region may also be used by the processor654 to verify the relationship between breathing feature and targetposition (e.g., external-internal correlation model). If a result of theverification process indicates that the model is inaccurate, theprocessor 654 may update (e.g., modify, recreate, etc.) the relationshipbetween breathing feature and target position (e.g., external-internalcorrelation model), so that the updated relationship may be used by thesystem 610 to deliver additional radiation to the patient 628 (e.g., tocontrol the radiation source, collimator, gantry, and/or patientsupport). In other embodiments, the processor 654 may cause theradiation process to stop if the result of the verification processindicates that the model is inaccurate.

In other embodiments, the image(s) of the internal target regiondetermined from the method 700 may be used by the processor 654 todetermine the position of the internal target region using stereoimaging technique. In stereo imaging technique, a set of referenceimages are first obtained. The reference images may be obtained beforethe treatment process begins. Each of the reference images is obtainedwhen the internal target region is at a certain position, and therefore,each reference image is associated with a certain position of the targetregion. In some embodiments, the reference images may be generated usinga CT system by rotating the radiation source of the CT system atdifferent gantry angles while the target is undergoing motion. Thus, thereference images are obtained at different times. In other embodiments,if the system 610 has imaging capability, the reference images may begenerated using the system 610. In some embodiments, after the image(input image) from the method 700 is obtained, the processor 654 thenselects one or more reference images from the reference image set thatspatially correspond with the input image. In one technique, theprocessor 654 determines a projection line that extends between thesource that generates the input image and the target image in the imageframe. The processor 654 also determines a plurality of projection linesfor respective reference images, wherein each projection line extendsbetween the source and the target image in the corresponding referenceimage. The processor 654 then determines, for each projection line, anepipolar distance that is between the projection line of the input imageand the projection line for the corresponding reference image. Theepipolar distance is measured in a direction that is perpendicular toboth the projection line of the input image and the projection line ofthe reference image. In some embodiments, the processor 654 isconfigured to select a reference image that spatially corresponds withthe input image by comparing the epiploar distances with a prescribedthreshold. If the epipolar distance for a reference image is below theprescribed threshold, then it may be determined that the target'sposition when the input image is generated (during method 700)corresponds (e.g., is the same relative to certain arbitrary coordinatesystem) with the target's position when the reference image isgenerated. In such cases, the processor 654 then selects such referenceimage for determining the position of the target region. In someembodiments, the position of the midpoint at the epipolar line betweenthe projection line of the input image and the projection line of theselected reference image may be used as the position of the target.Stereo imaging technique has been described in U.S. patent applicationSer. No. 12/211,686, filed on Sep. 16, 2008, the entire disclosure ofwhich is expressly incorporated by reference herein.

It should be noted that using detected non-periodicity of patient'sbreathing to trigger an imaging of internal region is advantageousbecause it obviates the need to periodically image the internal regionfor verification of the position of the internal region and forverification of the relationship between breathing and target positions.Periodic imaging of internal region is not desirable because itcomplicates the treatment procedure. Also, in the case in whichradiation is used to image internal region, periodic imaging usingradiation is also not desirable because it increases the radiationdosage to the patient 628.

As discussed, in other embodiments, the system 610 may include anadditional imaging device. FIG. 8 illustrates a variation of the system610 that further includes an additional imaging device 680 in accordancewith some embodiments. In the illustrated embodiments, the imagingdevice 680 includes a diagnostic radiation source 682 and an imager 684opposite from it. In the illustrated embodiments, the radiation source620 is configured to provide treatment radiation, and the diagnosticradiation source 682 is configured for generating image(s) using lowenergy beam (e.g., kV imaging system). The radiation sources 620, 682are integrated into a same gantry 612 (e.g., oriented relative to eachother at 90°), or alternatively, may be separate devices that are placedadjacent to each other, and may be rotated at different speeds. In otherembodiments, instead of coupling the radiation sources 620, 682 to thearm gantry 612, the radiation sources 620, 682 may be coupled to acommon ring gantry, or to different respective ring gantries that can berotated together or relative to each other. The method of using thesystem of FIG. 8 is similar to that described previously with referenceto FIG. 6.

In further embodiments, instead of using the breathing monitoring system10 with a device that has treatment capability, the breathing monitoringsystem 10 may be used with an imaging device. FIG. 9 illustrates acomputed tomography system 910 that is used with the breathingmonitoring system 10 in accordance with some embodiments. The system 910includes a gantry 912, and a support 914 for supporting a patient 928.The gantry 912 includes an x-ray source 920 that projects a beam 926 ofx-rays towards a detector 924 on an opposite side of the gantry 912while the patient 928 is positioned at least partially between the x-raysource 920 and the detector 924. By means of non-limiting examples, thebeam of x-rays can be a cone beam or a fan beam. The detector 924 has aplurality of sensor elements configured for sensing a x-ray that passesthrough the patient 928. Each sensor element generates an electricalsignal representative of an intensity of the x-ray beam as it passesthrough the patient 928.

The system 910 also includes a control system 918. In the illustratedembodiments, the control system 918 includes a processor 954, such as acomputer processor, coupled to a control 940. The control system 918 mayalso include a monitor 956 for displaying data and an input device 958,such as a keyboard or a mouse, for inputting data. The operation of theradiation source 920 and the gantry 912 are controlled by the control940, which provides power and timing signals to the radiation source920, and controls a rotational speed and position of the gantry 912,based on signals received from the processor 954. Although the control940 is shown as a separate component from the gantry 912 and theprocessor 954, in alternative embodiments, the control 940 can be a partof the gantry 912 or the processor 954. The processor 954 may be theprocessor 14, or may include features implemented in the processor 14 ofthe breathing monitoring system 10. In such cases, the radiation system910 and the breathing monitoring system 10 share the same processor orparts of a same processor. Alternatively, the processor 954 may be adifferent processor from the processor 14.

It should be noted that the system 910 is not limited to theconfiguration described above, and that the system 910 may have otherconfigurations in other embodiments. For example, in other embodiments,the system 910 may have a different shape. In other embodiments, theradiation source 920 of the system 910 may have different ranges ofmotions and/or degrees of freedom. For example, in other embodiments,the radiation source 920 may be rotatable about the patient 928completely through a 360° range, or partially through a range that isless than 360°. Also, in other embodiments, the radiation source 920 istranslatable relative to the patient 928. Further, the radiation source920 is not limited to delivering diagnostic energy in the form of x-ray,and may deliver treatment energy for treating a patient.

During a scan to acquire x-ray projection data (i.e., CT image data),the gantry 912 rotates about the patient 928 at different gantry angles,so that the radiation source 920 and the imager 924 may be used toobtain images at different gantry angles. As the system 910 is operatedto obtain images at different gantry angles, the patient 928 isbreathing. Thus, the resulting images at different gantry angles maycorrespond to different phases of a breathing cycle for the patient 928.After the scan is completed, the projection images at different gantryangles are stored, e.g., in a memory (such as a non-transitory medium),and the projection images are processed to sort the images so thatimages at different gantry angles that correspond to a same phase of abreathing cycle are binned (e.g., associated with each other). Thebinned images for a specific phase of a respiratory cycle can then beused to generate a reconstructed three-dimensional CT image for thatphase.

In some embodiments, when using the system 910 of FIG. 9, the radiationsource 920 is rotated about the patient 928 to deliver diagnostic(imaging) radiation from a plurality of gantry angles. As radiation isbeing delivered to the patient 928, the breathing monitoring system 10of FIG. 1 may be used to monitor the breathing of the patient 928. Insome embodiments, the processor 954 processes the signals from thecamera to determine breathing amplitudes of the patient 928, and thengates the delivery of the imaging radiation based on the amplitudes. Forexample, the processor 954 may cause the radiation source 920 to deliverradiation, or to stop a delivery of radiation, when the determinedamplitude is within a prescribed amplitude range. In other embodiments,the processor 954 processes the signals from the camera to determinerespiratory phases of the patient 928, and then gates the delivery ofthe radiation based on the respiratory phases. For example, theprocessor 954 may cause the radiation source 920 to deliver radiation,or to stop a delivery of radiation, when the determined phase is withina prescribed phase range. In other embodiments, instead of, or inaddition to, controlling the delivery of radiation, the processor 954may be configured to control the gantry 912 (e.g., stop, accelerate, ordecelerate the gantry 912), and/or to position the patient support 914,based on the determined amplitude and/or phase.

In other embodiments of a method of using the system 10 with theradiation system 610, the processor 954 is configured to detectnon-periodicity in the patient's 928 breathing using the techniquedescribed with reference to FIG. 2. When the processor 954 determinesthat there is non-periodicity in the patient's 928 breathing, theprocessor 954 may generate a signal (e.g., a beam-stop signal) to causethe radiation source 920 to stop delivering radiation, a signal tocontrol a motion of the gantry 912 (e.g., to stop the gantry, deceleratethe gantry 912, or accelerate the gantry 912), and/or a signal toposition the patient support 914.

Computer System Architecture

FIG. 10 is a block diagram that illustrates an embodiment of a computersystem 1900 upon which an embodiment of the invention may beimplemented. Computer system 1900 includes a bus 1902 or othercommunication mechanism for communicating information, and a processor1904 coupled with the bus 1902 for processing information. The processor1904 may be an example of the processor 14 of FIG. 1, or anotherprocessor that is used to perform various functions described herein. Insome cases, the computer system 1900 may be used to implement theprocessor 14 (or other processors described herein). The computer system1900 also includes a main memory 1906, such as a random access memory(RAM) or other dynamic storage device, coupled to the bus 1902 forstoring information and instructions to be executed by the processor1904. The main memory 1906 also may be used for storing temporaryvariables or other intermediate information during execution ofinstructions to be executed by the processor 1904. The computer system1900 further includes a read only memory (ROM) 1908 or other staticstorage device coupled to the bus 1902 for storing static informationand instructions for the processor 1904. A data storage device 1910,such as a magnetic disk or optical disk, is provided and coupled to thebus 1902 for storing information and instructions.

The computer system 1900 may be coupled via the bus 1902 to a display1912, such as a cathode ray tube (CRT) or a flat panel, for displayinginformation to a user. An input device 1914, including alphanumeric andother keys, is coupled to the bus 1902 for communicating information andcommand selections to processor 1904. Another type of user input deviceis cursor control 1916, such as a mouse, a trackball, or cursordirection keys for communicating direction information and commandselections to processor 1904 and for controlling cursor movement ondisplay 1912. This input device typically has two degrees of freedom intwo axes, a first axis (e.g., x) and a second axis (e.g., y), thatallows the device to specify positions in a plane.

The computer system 1900 may be used for performing various functions(e.g., calculation) in accordance with the embodiments described herein.According to one embodiment, such use is provided by computer system1900 in response to processor 1904 executing one or more sequences ofone or more instructions contained in the main memory 1906. Suchinstructions may be read into the main memory 1906 from anothercomputer-readable medium, such as storage device 1910. Execution of thesequences of instructions contained in the main memory 1906 causes theprocessor 1904 to perform the process steps described herein. One ormore processors in a multi-processing arrangement may also be employedto execute the sequences of instructions contained in the main memory1906. In alternative embodiments, hard-wired circuitry may be used inplace of or in combination with software instructions to implement theinvention. Thus, embodiments of the invention are not limited to anyspecific combination of hardware circuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to the processor 1904 forexecution. Such a medium may take many forms, including but not limitedto, non-volatile media, volatile media, and transmission media.Non-volatile media includes, for example, optical or magnetic disks,such as the storage device 1910. A non-volatile medium may be consideredas an example of a non-transitory medium. Volatile media includesdynamic memory, such as the main memory 1906. A volatile medium may beconsidered as another exampler of a non-transitory medium. Transmissionmedia includes coaxial cables, copper wire and fiber optics, includingthe wires that comprise the bus 1902. Transmission media can also takethe form of acoustic or light waves, such as those generated duringradio wave and infrared data communications.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, a RAM, a PROM, and EPROM,a FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to the processor 1904 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to the computer system 1900can receive the data on the telephone line and use an infraredtransmitter to convert the data to an infrared signal. An infrareddetector coupled to the bus 1902 can receive the data carried in theinfrared signal and place the data on the bus 1902. The bus 1902 carriesthe data to the main memory 1906, from which the processor 1904retrieves and executes the instructions. The instructions received bythe main memory 1906 may optionally be stored on the storage device 1910either before or after execution by the processor 1904.

The computer system 1900 also includes a communication interface 1918coupled to the bus 1902. The communication interface 1918 provides atwo-way data communication coupling to a network link 1920 that isconnected to a local network 1922. For example, the communicationinterface 1918 may be an integrated services digital network (ISDN) cardor a modem to provide a data communication connection to a correspondingtype of telephone line. As another example, the communication interface1918 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN. Wireless links may also beimplemented. In any such implementation, the communication interface1918 sends and receives electrical, electromagnetic or optical signalsthat carry data streams representing various types of information.

The network link 1920 typically provides data communication through oneor more networks to other devices. For example, the network link 1920may provide a connection through local network 1922 to a host computer1924 or to equipment 1926 such as a radiation beam source or a switchoperatively coupled to a radiation beam source. The data streamstransported over the network link 1920 can comprise electrical,electromagnetic or optical signals. The signals through the variousnetworks and the signals on the network link 1920 and through thecommunication interface 1918, which carry data to and from the computersystem 1900, are exemplary forms of carrier waves transporting theinformation. The computer system 1900 can send messages and receivedata, including program code, through the network(s), the network link1920, and the communication interface 1918.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. For example, the term “image” needs not belimited to an image that is displayed visually, and may refer to imagedata that is stored. Also, the term “processor” may include one or moreprocessing units, and may refer to any device that is capable ofperforming mathematical computation implemented using hardware and/orsoftware. The term “processor” may also refer to software stored in anon-transitory medium in other embodiments. Further, in any of theembodiments described herein, instead of using the processor 14/654/954to perform the various functions described, a separate processor may beused. The specification and drawings are, accordingly, to be regarded inan illustrative rather than restrictive sense. The present inventionsare intended to cover alternatives, modifications, and equivalents,which may be included within the spirit and scope of the presentinventions as defined by the claims.

What is claimed:
 1. A method of triggering an imaging process,comprising: obtaining breathing signals, the breathing signalsrepresenting a breathing of a subject that fluctuates in amplitude inresponse to the subject breathing freely, wherein the breathing signalsare generated in a period during which the subject is allowed to breathefreely; analyzing the breathing signals to identify a non-periodicity inthe breathing of the subject, wherein the identified non-periodicity isa deviation from a normal breathing pattern, the deviation beingcharacterized as to exclude gradual breathing pattern variation thatoccurs over time; and after the non-periodicity has occurred, generatinga signal to cause an imaging process to begin in response to theidentified non-periodicity; wherein the acts of analyzing and generatingare performed during a radiation treatment procedure; and wherein themethod further comprises using an image from the imaging process toverify an item for the radiation treatment procedure.
 2. The method ofclaim 1, wherein the act of analyzing the breathing signals comprisesusing a signal-phase histogram.
 3. The method of claim 2, furthercomprising generating the signal-phase histogram, wherein thesignal-phase histogram is generated by obtaining a plurality ofsignal-phase points, wherein each of the signal-phase points comprises aphase of a respiratory cycle and a signal amplitude.
 4. The method ofclaim 3, further comprising updating the signal-phase histogram byremoving one or more of the signal-phase points in the signal-phasehistogram that are older than a prescribed number of breathing cycle(s).5. The method of claim 2, wherein the act of analyzing the breathingsignals comprises determining if a current signal-phase point or apredicted signal-phase point is within a prescribed range from anaverage value calculated using data points in the signal-phasehistogram.
 6. The method of claim 2, wherein the act of analyzing thebreathing signals comprises determining if a current signal-phase pointor a predicted signal-phase point is within a prescribed range from amedian value calculated using data points in the signal-phase histogram.7. The method of claim 1, further comprising generating a stop-signal tostop a delivery of a treatment radiation beam during the radiationtreatment procedure in response to the identified non-periodicity. 8.The method of claim 1, wherein the imaging process comprises a CTimaging procedure, a MRI procedure, a PET procedure, a SPECT procedure,a x-ray procedure, an ultrasound procedure, or a tomosynthesis imagingprocedure.
 9. The method of claim 1, wherein the act of obtaining thebreathing signals comprises using a camera.
 10. The method of claim 1,wherein the act of using the image to verify an item comprises using theimage to verify a position of a target inside the subject's body. 11.The method of claim 1, wherein the act of using the image to verify anitem comprises using the image to verify a model for correlating aposition of a target inside the subject's body with a phase of arespiratory cycle.
 12. The method of claim 1, wherein the identifiednon-periodicity comprises a predicted non-periodicity.
 13. The method ofclaim 1, further comprising performing the imaging process, wherein theimaging process is performed using a gating technique.
 14. A computerproduct having a set of instructions stored in a non-transitory medium,wherein an execution of the instructions causes a method to beperformed, the method comprising: obtaining breathing signalsrepresenting a breathing of a subject that fluctuates in amplitude inresponse to the subject breathing freely, wherein the breathing signalsare generated in a period during which the subject is allowed to breathefreely; analyzing the breathing signals to identify a non-periodicity inthe breathing of the subject, wherein the identified non-periodicity isa deviation from a normal breathing pattern, the deviation beingcharacterized as to exclude gradual breathing pattern variation thatoccurs over time; and after the non-periodicity has occurred, generatinga signal to cause an imaging process to begin in response to theidentified non-periodicity; wherein the acts of analyzing and generatingare performed during a radiation treatment procedure; and wherein themethod further comprises using an image from the imaging process toverify an item for the radiation treatment procedure.
 15. The computerproduct of claim 14, wherein the act of analyzing the breathing signalscomprises using a signal-phase histogram.
 16. The computer product ofclaim 15, wherein the method further comprises generating thesignal-phase histogram, wherein the signal-phase histogram is generatedby obtaining a plurality of signal-phase points, wherein each of thesignal-phase points comprises a phase of a respiratory cycle and asignal amplitude.
 17. The computer product of claim 15, wherein the actof analyzing the breathing signals comprises determining if a currentsignal-phase point or a predicted signal-phase point is within aprescribed range from an average value calculated using data points inthe signal-phase histogram.
 18. The computer product of claim 15,wherein the act of analyzing the breathing signals comprises determiningif a current signal-phase point or a predicted signal-phase point iswithin a prescribed range from a median value calculated using datapoints in the signal-phase histogram.
 19. The computer product of claim14, wherein the method further comprises generating a stop-signal tostop a delivery of a treatment radiation beam during the radiationtreatment procedure in response to the identified non-periodicity. 20.The computer product of claim 14, wherein the act of using the image toverify an item comprises using the image to verify a position of atarget inside the subject's body.
 21. The computer product of claim 14,wherein the act of using the image to verify an item comprises using theimage to verify a model for correlating a position of a target insidethe subject's body with a phase of a respiratory cycle.
 22. A system fortriggering an imaging process, comprising: a breathing monitoringdevice; and a processor comprising at least some hardware, the processorconfigured for: obtaining, from the breathing monitoring device,breathing signals representing a breathing of a subject that fluctuatesin amplitude in response to the subject breathing freely, wherein thebreathing signals are generated in a period during which the subject isallowed to breathe freely; analyzing the breathing signals to identify anon-periodicity in the breathing of the subject, wherein the identifiednon-periodicity is a deviation from a normal breathing pattern, thedeviation being characterized as to exclude gradual breathing patternvariation that occurs over time; and generating a signal to cause animaging process to begin in response to the identified non-periodicityafter the non-periodicity has occurred; wherein the processor isconfigured to perform the acts of analyzing and generating during aradiation treatment procedure; and wherein the processor is furtherconfigured to use an image from the imaging process to verify an itemfor the radiation treatment procedure.
 23. The system of claim 22,wherein the processor is configured for analyzing the breathing signalsby using a signal-phase histogram.
 24. The system of claim 23, whereinthe processor is further configured for generating the signal-phasehistogram by obtaining a plurality of signal-phase points, wherein eachof the signal-phase points comprises a phase of a respiratory cycle anda signal amplitude.
 25. The system of claim 23, wherein the processor isconfigured to perform the act of analyzing the breathing signals bydetermining if a current signal-phase point or a predicted signal-phasepoint is within a prescribed range from an average value calculatedusing data points in the signal-phase histogram.
 26. The system of claim23, wherein the processor is configured to perform the act of analyzingthe breathing signals by determining if a current signal-phase point ora predicted signal-phase point is within a prescribed range from amedian value calculated using data points in the signal-phase histogram.27. The system of claim 23, wherein the processor is further configuredfor generating a stop-signal to stop a delivery of a treatment radiationbeam during the radiation treatment procedure in response to theidentified non-periodicity.
 28. The system of claim 22, wherein the itemcomprises a position of a target inside the subject's body, and theprocessor is configured to use the image to verify the position of thetarget inside the subject's body.
 29. The system of claim 22, whereinthe item comprises a model for correlating a position of a target insidethe subject's body with a phase of a respiratory cycle, and theprocessor is configured to use the image to verify the model.